This invention relates to a device that produces a mechanical movement, and, more particularly, to a mechanical actuator that moves between two positions and is stable in either of the two positions without the application of power.
A mechanical actuator is a device that controllably produces a mechanical movement. The mechanical actuator is typically connected to another device which requires such a movement for its proper operation. Mechanical actuators can be designed to produce linear, rotational, or other types of movements, as required.
In one application, the mechanical actuator produces movement between one of two states, without any need for controllable positioning between the two states. In an example, a mechanical shutter is either open or closed. The mechanical actuator that drives the shutter operates between one state corresponding to the closed shutter and the other state corresponding to the open shutter. An intermediate state is of no interest, and in fact it is desirable in many applications that the shutter move as rapidly as possible between the open and closed states, with little time spent in the partially open state. Another example is an electrically driven mechanical lock, such as a door or trunk lock of an automobile, where in the case of a power failure a charged capacitor bank provides an electrical impulse to open the lock. The only states of interest are the locked and unlocked conditions. In this case, it is desirable that the selected state be retained even in the absence of power.
A solenoid or other type of electromagnet-driven device is often used as a mechanical actuator operating between two states. However, such devices require the continuous application of power or the provision of a separate latching/unlatching mechanism. For some situations, the continuous power utilization is unacceptable because of the high power consumption, heat generation, or other reasons. The solenoid produces force on one direction only, and the first state is achieved using a return spring whose force must be overcome to achieve the first state. The result is that the holding forces in the two states are greatly different, and also that a considerable power consumption may be required to hold the mechanism in the first state. If power is lost, the actuator moves to the second state dictated by the operation of the return spring.
There is, accordingly, a need for an improved mechanical actuator for operation between two states. The present invention fulfills this need, and further provides related advantages.
The present invention provides a mechanical actuator that operates reliably and rapidly between two states. The actuator remains in either selected state when the driving power is removed, allowing the selected state to be retained without power consumption and heat production. The selected state is also retained through a power loss. No separate latching/unlatching mechanism is required. The force applied to retain the mechanism in the selected state can be the same for both states, or it can be made unequal. The mechanism can be made to switch between states quite rapidly.
In accordance with the invention, an actuator comprises a bipolar electromagnet and a ferromagnetic plunger disposed adjacent to the electromagnet and movable with respect to the electromagnet along an actuation axis. The plunger has a first end face and a second end face. A first permanent magnet is positioned remote from the electromagnet and in facing relation to the first end face of the plunger, and a second permanent magnet is positioned remote from the electromagnet and in facing relation to the second end face of the plunger. The plunger is slidable along the actuation axis between a first position with the first end face adjacent to the first permanent magnet and a second position with the second end face adjacent to the second permanent magnet.
In a preferred form, the actuator is cylindrically symmetric. In this form, an actuator comprises an annular bipolar electromagnet having a bore therethrough with a bore axis, and a ferromagnetic plunger disposed within the bore and slidable therein. The plunger has a first end face and a second end face. A first permanent magnet is positioned outside of the bore and in facing relation to the first end face of the plunger, and a second permanent magnet is positioned outside of the bore and in facing relation to the second end face of the plunger. The plunger is slidable in the bore between a first position with the first end face adjacent to the first permanent magnet and a second position with the second end face adjacent to the second permanent magnet.
In each case, a stop is desirably positioned between each face of the plunger and its respective permanent magnet. The stop is preferably made of an elastomer to cushion the impact of the plunger face against the permanent magnet. A push rod typically extends from one or both ends of the plunger, to provide connection to the device being actuated. The retention force in either state can be controlled by providing permanent magnets of the same or different forces, or by providing a biasing spring reacting between the electromagnet and the plunger. The entire apparatus is conveniently packed within a housing having sides and end plates, with appropriate openings in the end plates to permit pass-through of the push rods.
The actuator is operated using a bipolar power supply to energize the electromagnet. When the electromagnet is energized in the first direction, the plunger is driven toward the first permanent magnet. If the power is thereafter removed, the plunger is retained in this first position by the magnetic force of the first permanent magnet. The plunger is driven toward the second state by energizing the electromagnet in the second direction, to overcome the retention force of the first permanent magnet and to create a magnetic-induction repulsion force between the permanent magnetic field and the magnetized plunger. After reaching the second state, the plunger is retained by the force of the second permanent magnet. The retention force is controllably increased, where desired, by maintaining the energization of the electromagnet in addition to the induced permanent magnetic field in the plunger.